1. Field of the Invention
The invention relates to a method of and an apparatus for curing an optical disc D, more particularly to a method of and an apparatus for curing an ultraviolet curing resin R efficiently and uniformly, which resin is sandwiched between two disc substrates constituting the optical disc D.
2. Description of the Related Art
Generally, an optical disc D has an information signal therein such as an image, sound, or the like which is transferred onto one side of a disc substrate made of polycarbonate in the form of signal pits (signal holes).
In a relatively simple structure of an optical disc D, a metallic reflection film made of, e.g. aluminum, is provided on the surface of the signal pits, and a protection film such as an ultraviolet curing resin R film is formed on the metallic reflection film for preventing damage to the metallic reflection film.
However, as an optical disc D, such as a DVD, having a large storage capacity for information has recently become popular, the structure of disc substrates constituting the optical disc D is multilayered and becomes complex.
For example, in a random access memory type DVD, a twin surassite, a tellurium layer, a reflection film, a protection film and so forth are formed on the resin substrate.
Further, if the structure of the disc substrate becomes complex, there occurs a case where ultraviolet does not at all pass through the disc substrate.
Meanwhile, an optical disc D is formed of a first substrate to which information is applied as mentioned above, and a second disc substrate which are bonded to each other using an ultraviolet adhesive. A method of bonding these two disc substrates is described simply hereinafter.
An ultraviolet curing resin R is first applied to at least one of two disc substrates at the portion where it is joined with another disc substrate so as to bond two disc substrates.
After the adhesive is applied to the joining portion of the two disc substrates, both the disc substrates are rotated while they are bonded, then the ultraviolet curing resin R is distributed or developed uniformly between the two disc substrates.
Thereafter, ultraviolet is irradiated from the upper portion of the disc substrate so as to cure the adhesive, thereby obtaining an optical disc D formed of the two disc substrates which are bonded firmly.
When disc substrates have a complex structure through which ultraviolet does not transmit, even if ultraviolet is irradiated from the upper portion of the optical disc D, the ultraviolet curing resin R serving as an adhesive is not cured.
Even if disc substrates through which ultraviolet hardly transmits are used, if characters or patterns are printed on the disc substrates, there occurs a lack of uniformity when ultraviolet transmits through the disc substrates, so that the ultraviolet curing resin R is not efficiently and uniformly cured.
If there occurs a problem in the curing of the ultraviolet curing resin R, it causes the occurrence of strain or distortion such as warp, tilt, and exfoliation of the disc substrates when the optical disc D is manufactured.
The invention has been made to solve the foregoing problems.
That is, it is an object of the invention to provide a method of and an apparatus for curing an optical disc D capable of curing an ultraviolet curing resin R serving as an adhesive efficiently even if the optical disc D employs disc substrates through which ultraviolet does not transmit.
It is another object of the invention to provide a method and an apparatus for curing an optical disc D capable of curing an ultraviolet curing resin R serving as an adhesive efficiently even if the optical disc D employs disc substrates through which ultraviolet hardly transmits.
It is still another object of the invention to provide a method and an apparatus for curing an optical disc D capable of curing an ultraviolet curing resin R serving as an adhesive efficiently and uniformly if the optical disc D employs disc substrates on which printing or the like is applied.
To achieve the above objects, the inventors of this application endeavored themselves to study the foregoing problems and have found that an ultraviolet curing resin R serving as an adhesive can be efficiently cured by limiting the direction of irradiation of ultraviolet relative to the optical disc D.
That is, a first aspect of the invention is an apparatus for curing an optical disc D placed on a rotary holding table and formed by bonding a first disc substrate and a second disc substrate by the medium of an ultraviolet curing resin R, and it is characterized in comprising an ultraviolet irradiation peripheral unit disposed around the rotary holding table for irradiating ultraviolet from the peripheral surface of the optical disc D toward the inner portion thereof so as to cure the ultraviolet curing resin.
A second aspect of the invention is an apparatus for curing an optical disc D formed by bonding a first disc substrate and a second disc substrate by the medium of an ultraviolet curing resin R, and it is characterized in comprising an ultraviolet irradiation peripheral unit disposed around the rotary holding table for irradiating ultraviolet from the peripheral surface of the optical disc D toward the inner portion thereof so as to cure the ultraviolet curing resin, and an ultraviolet irradiation central unit disposed at the center of the rotary holding table for irradiating ultraviolet from the central hole of the optical disc D toward the outer portion thereof so as to cure the ultraviolet curing resin.
A third aspect of the invention is the apparatus for curing an optical disc D characterized in that the ultraviolet irradiation peripheral unit in the first or second aspect of the invention comprises a plurality of divided units which are disposed around the rotary holding table.
A fourth aspect of the invention is the apparatus for curing an optical disc D characterized in that the ultraviolet irradiation peripheral unit in the first or second aspect of the invention comprises a plurality of divided units which are disposed around the rotary holding table, and wherein the irradiation direction of ultraviolet is changeable to a vertical or horizontal direction.
A fifth aspect of the invention is the apparatus for curing an optical disc D characterized in further comprising a boss elastically pressed and journaled by and attached to the central portion of the rotary holding table in the first or second aspect of the invention.
A sixth aspect of the invention is the apparatus for curing an optical disc D characterized in that the boss in the first or second aspect of the invention is provided on the center of the rotary holding table to be movable toward or away from the surface of the rotary holding table by suction force.
A seventh aspect of the invention is the apparatus for curing an optical disc D characterized in further comprising suction means provided on the rotary holding table and connected to a negative pressure source, wherein the suction means allows the boss to move toward or away from the rotary holding table and the optical disc D to be placed on and attached to the rotary holding table.
An eighth aspect of the invention is the apparatus for curing an optical disc D characterized in further comprising a press member for pressing the first and second disc substrates to each other.
A ninth aspect of the invention is the apparatus for curing an optical disc D characterized in that the ultraviolet irradiation peripheral unit is divided into eight, and wherein two divided bodies 2A of the ultraviolet irradiation peripheral unit 2 are arranged in parallel with each other and eight units are disposed square as a whole.
A tenth aspect of the invention is the apparatus for curing an optical disc D characterized in that the ultraviolet irradiation peripheral unit is clamped between the rotary holding table and the fastening member.
An eleventh aspect of the invention is the apparatus for curing an optical disc D characterized in that the ultraviolet irradiation central unit can be inserted into and detached from the central hole of the optical disc D which is set on the rotary holding table when it moves vertically.
A twelfth aspect of the invention is a method of curing an optical disc D formed by bonding a first disc substrate and a second disc substrate by the medium of an ultraviolet curing resin R comprising the steps of irradiating ultraviolet from the peripheral surface of the optical disc D toward the inner portion thereof while the optical disc D is rotated so as to cure the ultraviolet curing resin R.
A thirteenth aspect of the invention is a method of curing an optical disc D formed by bonding a first disc substrate and a second disc substrate by the medium of an ultraviolet curing resin R comprising the steps of irradiating ultraviolet from the peripheral surface of the optical disc D toward the inner portion thereof and also irradiating ultraviolet from the center of the optical disc D toward the outer portion thereof while the optical disc D is rotated so as to cure the ultraviolet curing resin R.
A fourteenth aspect of the invention is the method of curing an optical disc D characterized in that the irradiation of ultraviolet from the peripheral surface of the optical disc D toward the inner portion thereof is effected by an ultraviolet irradiation peripheral unit which is divided into plural units and the plural units are independent of one another.
A fifteenth aspect of the invention is the method of curing an optical disc D characterized in that the irradiation of ultraviolet from the peripheral surface of the optical disc D toward the inner portion thereof is effected by the ultraviolet irradiation peripheral unit which is divided into plural units, and the plural units are independent of one another for preventing localized shaded areas of ultraviolet due to foreign matter which is mixed in the ultraviolet curing resin R.
A sixteenth aspect of the invention is the method of curing an optical disc D characterized in that ultraviolet is irradiated while the first and second disc substrates are pressed against each other.
Although the invention has been described above, it is possible to employ a structure of the apparatus for curing an optical disc composed of a combination of the foregoing first to eleventh aspects of the invention or a structure of the method of curing an optical disc composed of a combination of the foregoing twelfth to sixteenth aspects of the invention.
Inasmuch as the invention has the above structure, it operates as follows.
Ultraviolet is irradiated from the peripheral surface of the optical disc D toward the inner portion thereof after the two disc substrates which are bonded to each other by the medium of the ultraviolet curing resin R are placed on the rotary holding table while the rotary holding table is rotated.
Ultraviolet is irradiated from the peripheral surface of the optical disc D toward the inner portion thereof and from the center, i.e., the central hole of the optical disc D, toward the outer portion thereof after the two disc substrates which are bonded to each other by the medium of the ultraviolet curing resin R are placed on the rotary holding table while the rotary holding table is rotated.